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authorDennis Zhou (Facebook) <dennisszhou@gmail.com>2018-08-31 16:22:44 -0400
committerJens Axboe <axboe@kernel.dk>2018-08-31 14:48:58 -0600
commit3111885015b458c97b4cf272e2a87f1d6f0ed06a (patch)
tree828379a8a4a92e45414f08b05a9e143d72e7d7ea /block
parent59b57717fff8b562825d9d25e0180ad7e8048ca9 (diff)
blkcg: use tryget logic when associating a blkg with a bio
There is a very small change a bio gets caught up in a really unfortunate race between a task migration, cgroup exiting, and itself trying to associate with a blkg. This is due to css offlining being performed after the css->refcnt is killed which triggers removal of blkgs that reach their blkg->refcnt of 0. To avoid this, association with a blkg should use tryget and fallback to using the root_blkg. Fixes: 08e18eab0c579 ("block: add bi_blkg to the bio for cgroups") Reviewed-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Dennis Zhou <dennisszhou@gmail.com> Cc: Jiufei Xue <jiufei.xue@linux.alibaba.com> Cc: Joseph Qi <joseph.qi@linux.alibaba.com> Cc: Tejun Heo <tj@kernel.org> Cc: Josef Bacik <josef@toxicpanda.com> Cc: Jens Axboe <axboe@kernel.dk> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
-rw-r--r--block/bio.c3
-rw-r--r--block/blk-throttle.c5
2 files changed, 5 insertions, 3 deletions
diff --git a/block/bio.c b/block/bio.c
index b12966e415d3..8c680a776171 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -2015,7 +2015,8 @@ int bio_associate_blkg(struct bio *bio, struct blkcg_gq *blkg)
{
if (unlikely(bio->bi_blkg))
return -EBUSY;
- blkg_get(blkg);
+ if (!blkg_try_get(blkg))
+ return -ENODEV;
bio->bi_blkg = blkg;
return 0;
}
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index a3eede00d302..01d0620a4e4a 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -2129,8 +2129,9 @@ static inline void throtl_update_latency_buckets(struct throtl_data *td)
static void blk_throtl_assoc_bio(struct throtl_grp *tg, struct bio *bio)
{
#ifdef CONFIG_BLK_DEV_THROTTLING_LOW
- if (bio->bi_css)
- bio_associate_blkg(bio, tg_to_blkg(tg));
+ /* fallback to root_blkg if we fail to get a blkg ref */
+ if (bio->bi_css && (bio_associate_blkg(bio, tg_to_blkg(tg)) == -ENODEV))
+ bio_associate_blkg(bio, bio->bi_disk->queue->root_blkg);
bio_issue_init(&bio->bi_issue, bio_sectors(bio));
#endif
}